The present invention concerns a water retention net which is mainly utilized, for example, in greening stabilization of slopes or the like, greening treatment of deserts, cultivation of agricultural plants and the like.
Heretofore, in a vegetation treatment with an aim of protection and greening stabilization of slopes, nets made of metal mesh or synthetic resin materials have been used in which the nets are laid over the slopes to prevent falling of soils and sands and then vegetation materials such as seeds and brought-in soils are sprayed.
However, since nets used generally have scarce water retentivity by themselves and tend to be dried and, accordingly, water required for growing plants can not be supplied enough for slopes in little rainfall districts or in arid places, so that it has been necessary to append non-woven fabrics retaining a water retention agent. Alternatively, it has been necessary to admix the water retention agent per se, for example, with brought-in soils.
Further, in recent years, use of steric structure nets in which string portions forming the net mesh are constituted into a wall or like other steric structure has been considered in the vegetation treatment with an aim of preventing the vegetation materials from being flushed away or scattered easily by window and rainfall or falling together with soils and sands (for example, JP-A-03183820(Japanese Patent Laid-Open Hei 3-183820)).
However, even in such nets, since constituent yarns are made, for example, of synthetic resin monofilaments and scarcely have water absorbing property by themselves, no sufficient water retention can be provided by the nets alone.
Further, if the net mesh is made excessively fine, it rather hinders fixation and growing of plants, increases the amount of yarns used, makes the net heavy and difficult to handle with, and expensive as well.
Furthermore, for the greening of deserts, porous pipe materials are buried underground or arranged on the surface of the ground and water is passed through the pipes to supply water to surface ground layers for instance. However, this results in problems that control for the amount of water supply is difficult and water supply is localized or partialized and it is difficult to economize water because of water evaporation.
Further, while it has been attempted to improve the water retentivity by directly mixing, for example, water absorbing resin polymers into soils and sands of deserts. However, since there is a difference in the specific gravity between the water absorbing resin polymers and soils and sands, they are not mixed uniformly but tend to be localized, so that it is difficult to ensure uniform water retention over the entire area. Further, since the water absorbing resin polymers are poor in the weather resistance, it is almost impossible to use them for long years with no loss of the water retaining effect.
The present invention has been accomplished in view of the foregoings and intends to provide a water retention net having a water retentivity not obtainable in conventional nets and capable of being used suitably to water retention or water absorption in vegetation treatment for slopes, greening treatment for deserts or green treatment of cities, particularly, in steric structure nets as well as in usual nets made of synthetic fiber yarns.
The water retention net according to the present invention for solving the foregoing subjects comprises a net prepared by warp-knitting in which a water absorbing resin or a water retention agent mainly comprising the resin is deposited to a string portion forming a net mesh.
According to the water retention net of the present invention, since the water absorbing resin or the water retention agent mainly comprising the resin is deposited to the string portion forming the net mesh, water given by spraying or rainfall or water in the ground or air is absorbed and retained in the water retention agent. Particularly, in the net prepared by warp-knitting, since the string portion comprises a continuous sequence of knit meshes, the water retention agent is easily retained in the knit mesh opening portion to increase the amount of water retained. Further, thus retained water is gradually released. Accordingly, a satisfactory function of supplying water can be provided by laying the net, for example, on the slopes of arid places or waste lands.
The water retention net of the invention is a steric structure net in which the string portion forming the net mesh has a steric shape having air transmittable and water transmittable gap spaces wherein the water absorbing resin or the water retention agent mainly comprising the resin is deposited at least on one side substantially over the entire area thereof.
According to the water retention net of the present invention, since the net constitutes, as a whole, a steric structure having a required thickness, it possesses satisfactory air transmittability and water transmittability by the possession of gap spaces in the steric string portion. In addition, since the water retention agent is deposited at least on one side of the net, it has excellent water retentivity in the same manner as described above. Therefore, when it is laid and used, for example, on the slopes of arid places or waste lands, it has an effect of preventing falling of soils and sands and vegetation materials by the net and provides a satisfactory function of supplying water.
In the steric structure net, according to the invention the string portion is constituted into a steric shape having air transmittable and water transmittable gap spaces with front and back fabric portions knitted at a width for one or plurality of wales respectively by warp knitting and connecting yarns for connecting both of the fabric portions, and the string portion is continuous in the knitting direction and knotted alternately with string portions which are in continuous on both sides in the front and back string portions respectively.
In this invention, not only satisfactory air transmittability and water transmittability can be ensured by the steric structure of the string portion defining the net mesh but also the water retention agent can be deposited concentrically by utilizing fine gap spaces and large surface area formed by knitting the front and back fabrics of the string portion. Therefore, the water absorption and water retention by the water retention agent, combined with the water retention by the assembly of the fibers, can increase the water retention as the entire net and, also in combination with the steric string portion that serves as the water supply channel, can provide a further excellent function of water supply.
Further, it is possible to use a steric structure net in which string portion formed by the front and back fabric portions and the connection yarns is knotted with adjacent string portions at the front and back fabric portions on every predetermined pitch in the continuing direction while being positionally displaced from each other, and the portions of the connection yarns for connecting the front and back fabric portions in each of the string portions are alternately inclined rightwardly and leftwardly to form a truss structure.
In this case, when load and pressure exert on the net in the direction of the thickness, they act so as to regulate the turning-down of the string portions to each other and the shape of the net mesh and the steric structure of the net are stabilized. That is, it is strong to the load and pressure in the direction of the thickness, excellent in the pressure resistance and shape retainability and has good. elastic force. Accordingly, also when it is buried and used underground, the string portion is not collapsed but keeps a steric state to possess a satisfactory water supply function.
Furthermore, even if a net mesh of a relatively large opening is formed, since the ratio of area occupied by the string portions is considerably large for the entire net in average and the surface area for the yarns constituting the net is also large, a great amount of the water retention agent can be deposited and retained by so much to further enhance the water retaining effect.
In the steric structure net in each of the inventions, the yarns forming mesh at least in the front and back fabric portions are suitably comprised of a plurality of aligned monofilament yarns, multifilament yarns of synthetic resin or yarns comprising a combination of them.
That is, since the fiber density for the front and back fabric portions of the string portion is increased by the constitution described above and, although this is a net, the water retention agent or the adhesive containing the water retention agent deposited by the coating means such as dipping intrudes as far as the inside of the string portion and is deposited so as to wrap the constituent yarns, the water retention agent can be retained more stably. Particularly, the retention of the water retention agent is satisfactory in a state of absorbing water and swelling to increase the volume. Therefore, if it is used being laid on the slopes or buried underground, the water retention agent is not fallen easily.
Further, it may have a constitution in which a string portion not having connection yarns is provided so as to form a mesh opening smaller than that of the string portion having connection yarns for defining the net mesh opening space, in at least one of the front and back fabric portions in the steric structure net.
In this steric structure net, bending deformation or the like of the string portion defining the net mesh opening space can be restricted by the string portion not having the connection yarns, by which the steric state of the string portion defining the net mesh opening space and the shape of the net mesh opening space can be retained more preferably.
In each of the inventions, the water retention agent is preferably deposited to the net by a coating means such as dipping. For example, the water retention agent is mixed with a volatile solvent, water or other additive and deposited by coating to the net before it is solidified.
With such a constitution, the water retention agent can be deposited surely to the yarns constituting the net and retained without dropping easily during use and satisfactory water retentivity can be kept for a long period of time.
Further, the retention agent can also be mixed with an adhesive and deposited to the net by the coating means. As the adhesive, use of an aqueous adhesive is preferred with a view point for the effect of the water absorbing and water retaining effect.
In this case, even if the net constituting yarns are made of monofilaments of synthetic resin, the water retention agent is surely deposited and maintained by the adhesive and the water absorbing and water retaining property can be maintained satisfactorily for a long period of time.
Further, due to the deposition of the adhesive, binding strength between the yarns constituting the net is increased, stitches are less tend to be slackened, the steric structure is more stabilized, the elastic force and the compression resistance are increased, and the steric shape of the string portion defining the net mesh opening can be kept more easily even when the net mesh opening are formed to be large, so that the net mesh opening space is maintained in the steric shape and roots of plants extend easily through the net meshes.